The invention relates generally to the field of methods and means for inducing hypoxia symptoms in persons undergoing altitude flight training. More particularly, the invention relates to methods and means for inducing hypoxia by producing an enriched nitrogen and depleted oxygen atmosphere at moderately reduced pressures and in relatively short time frames in hypobaric chambers.
Hypoxia resulting from atmospheric oxygen partial pressures lower than normal can occur during aircraft flights. Hypoxia may occur at altitudes at or greater than approximately 10,000 feet above sea level. The early symptoms indicate a possible impending loss of consciousness, and it is therefore imperative that persons learn to recognize the onset of hypoxia in time to take precautionary measures--e.g., utilize an auxiliary source of oxygen or decrease the altitude of the aircraft--to remain conscious. It is standard aviation physiology training practice to induce hypoxia symptoms by utilizing a hypobaric chamber to reduce the internal atmospheric pressure, and thus the partial pressure of oxygen available to the trainees. For example, reduction of the atmospheric pressure within the chamber to approximately 5.46 psi matches the pressure to be encountered at an altitude of 25,000 feet above sea level. At this pressure the partial pressure of oxygen in the atmosphere within the chamber is low enough to induce hypoxia symptoms in the trainees. Because exposure to this low pressure will have to be maintained for a time period sufficient to induce the hypoxia symptoms, there is a significant documented risk of causing decompression sickness in the trainees. Pressures equivalent to greater than 18,000 feet above sea level create this potential for decompression sickness.
To reduce the risk of decompression sickness, routine practice includes a thirty minute pre-breathing period of oxygen, but this preventative method is not always successful. Additionally, the use of 100 percent oxygen is required within the chamber during the simulated ascent and descent.
It is important in training that conditions to be encountered in the real environment are simulated as accurately as possible. Thus the preferred method is to use a hypobaric chamber to provide reduced pressure and reduced oxygen partial pressure to the trainees, rather than merely reducing the oxygen content alone by breathing a low oxygen mixture through an oronasal mask. The lower pressure more accurately reflects the conditions encountered at high altitude and addresses other training objectives, such as practicing the valsalva maneuver. However, the concurrent incidents of decompression sickness accompanying this method create a loss of man-hours and result in significant medical expenditures.
It is an object of this invention to provide a method and means for inducing hypoxia symptoms without exposing the trainees to pressures equivalent to those encountered at greater than 18,000 feet above sea level, thus removing the risk of decompression sickness.
It is a further object to provide such a method and means which expose the trainees to a low pressure situation concurrent with an oxygen depleted atmosphere, such that the hypoxia demonstration will be realistic.
It is a further object to provide a method and means which can be utilized through changes made to existing hypobaric chambers.